Regenerative pyrolysis reactors are known for use in performing high temperature (e.g., >1200° C., or even >1500° C.) chemistry and cracking processes, including but not limited to execution of cyclic reverse flow reactor processes. Such high temperature pyrolysis processes may generally be referred to as regenerative pyrolysis reactor processes. Such processes include those reactions performed at temperatures higher than can suitably be performed in conventional steam crackers.
As with steam crackers, regenerative pyrolysis reactors are well suited for processing volatized or volatizable feedstocks that are substantially free of non-volatile components, such as metals, and other residual or nonvolatizable components, which would otherwise lay down, coke, ash, and/or build up in the reactor. Non-volatiles may be defined broadly herein to mean substantially any resid, metal, mineral, ash, ash-forming, asphaltenic, tar, coke, and/or other component or contaminant within the feedstock that will not vaporize below a selected boiling point or temperature and which, during or after pyrolysis, may leave an undesirable residue or ash within the reactor system, which is difficult to remove.
Typically, regenerative pyrolysis reactors may include a reactor bed or zone comprising some type of refractory material, such as but not limited to a thermal ceramic media or components where the reaction takes place within the reactor system. Conventional regenerative pyrolysis reactors typically may, for example, deliver a stream of fuel, oxidant, or a supplemental amount of one of these reactants, directly to a location somewhere within the flow path of the reactor bed. The delivered reactants then are caused to exothermically react therein and heat the reactor media or bed. Thereafter, the reaction products are exhausted and a pyrolysis feedstock, such as a vaporized hydrocarbon feed stream, is introduced into the heated region of the reactor media or bed, and exposed to the heated media to cause heating and pyrolysis of the feedstock. The pyrolyzed products are then removed from the reaction area and quenched in a quench region of the reactor system, to halt the pyrolysis reaction and yield a pyrolysis product.
However, as with steam cracking, economics may favor using lower cost feedstocks such as, by way of non-limiting examples, crude oil, heavy distillate cuts, contaminated naphthas and condensates, and atmospheric resids, as feedstocks for regenerative pyrolysis reactors. Unfortunately, these economically favored feedstocks typically contain undesirable amounts of nonvolatile components and have heretofore been unacceptable as regenerative reactor feedstocks. Generally, non-volatile concentrations (e.g., ash, metals, resids, etc.) in excess of 2 ppmw (ppm by weight) of metals in the feed stream to the reactor may cause significant fouling in a pyrolysis reactor. Some economically desirable lower cost feeds may contain in excess of 5 ppmw, or at least 2 wt %, or at least 3 wt %, or at least 5 wt % of nonvolatiles and may be considered an advantaged feed. Some advantages feeds may contain from at least 2 weight percent non-volatile components, and up to or even in excess of 10 percent by weight of non-volatiles, while still other feeds may contain well in excess of 10 weight percent of non-volatiles, even in excess of 20 weight percent, and even in excess of 50 weight percent, including significant quantities of high boiling point hydrocarbon resid, which is difficult to convert into useful chemical precursors. In conventional processes, the resid components are withdrawn as a bottoms stream and added to low value fuels, such as fuel oil.
Various techniques have been employed for treating petroleum hydrocarbon feeds for the removal of non-volatiles contained therein to render cost advantaged feeds suitable for various purposes. For example, U.S. Pat. No. 4,773,986 discloses increased severity visbreaking operations to remove a heavier phase in an amount of less than 15 wt. % and provide a remaining product having a Shell Hot Filtration number of less than 0.25, by treating product from the visbreaker to separate components that affect product stability by use of a promoter liquid or anti-solvent. U.S. Pat. No. 5,413,702 discloses a process of visbreaking residual oil to produce fuel oil or distillate, wherein visbreaking is conducted at high severity in a liquid phase, fluidized bed reactor with a hydrogen quench in the settling zone.
Other processes tend to improve the quality of hydrocarbon feeds containing non-volatiles for conventional steam cracking. However, in most instances the processes suffer from operating condition limitations, space limitations for retrofits, high capital costs, and high operating costs, due to the processing steps used, high capital expense of the required equipment, and/or unsatisfactory reduction limitations in the amount of non-volatiles removed from the feeds. Similar and even exaggerated problems exist for a regenerative pyrolysis reactor complex, due to their feed quality requirements and increased temperature severity.
The present invention provides a process for improving the quality of non-volatile-containing hydrocarbon feedstocks to render such feed suitable for use as a feedstream to a regenerative pyrolysis reactor system. The invention provides a commercially useful and cost effective technique for removing the ash-forming non-volatiles from the feedstock before the feedstock undergoes pyrolysis.